Sudden cardiac arrest (SCA) can kill a victim. Also called sudden cardiac death, SCA is a condition in which the heart stops pumping enough blood to sustain vital organs. SCA is usually caused by life-threatening arrhythmias, which are abnormalities in the heart's electrical system. The most common arrhythmia at the onset of SCA is ventricular fibrillation (VF). In this condition, the heart's muscle cells contract too chaotically to be effective in pumping blood to the brain and other vital organs. A SCA event is different than a heart attack, e.g., acute myocardial infarction (AMI), although a person suffering from a heart attack is more likely to develop abnormal heart rhythms and SCA.
SCA is one of the leading causes of death among adults worldwide: it kills approximately 225,000 people a year in the United States. SCA is largely unpredictable, with two out of every three deaths occurring outside of the hospital. Although existing heart disease is a common cause of SCA, many victims have never experienced any prior heart problems. Further, although risk of SCA increases with age, SCA can happen to anyone—even a child.
Treatment for SCA must be administered as soon as possible to increase chances of survival. In the initial few minutes of the SCA event, the probability of survival diminishes by approximately 10% each minute. Emergency medical services (EMS) personnel may not arrive quickly enough to administer effective treatment. This problem is worsened in remote or sparsely inhabited areas that delay response times. Every minute of delay diminishes the probability of saving a life.
Responding to a SCA event typically requires special equipment. The most critical equipment is a defibrillator, which applies an electrical shock that stops the fibrillation, resynchronizes cardiac activity, and restores a perfusing rhythm. In many instances the first defibrillator to reach the victim is an automated external defibrillator (AED). AEDs are sometimes made available for public use in places where many people congregate or are hard to reach by EMS personnel (for example, inside an airplane). People who work in such places that deploy AEDs usually receive training for operating the AED. In addition, people are starting to purchase AEDs for their homes. The person that could be resuscitated may be the person that bought the defibrillator, someone from his or her immediate family, or a guest in their home.
Existing AEDs are given a general configuration, e.g., programmed with settings such that they are suitable for use to treat any victim within the public at large. When an existing AED is applied to a victim, there are no data regarding the victim's normal cardiac rhythm. Further, the victim may be unconscious, so there is no way to know from the victim information about their medical history, emergency contact information, and the like.
Because existing AEDs are configured generally, they may perform less than optimally for particular victims in the public at large. For example, a particular victim may naturally have a fast and/or irregular cardiac rhythm, e.g., via conduction of paroxysmal atrial fibrillation. In this case, the defibrillator may misdiagnose the rhythm as requiring defibrillation therapy, and may control or recommend delivery of defibrillation therapy.